chore: consolidate platform split checks

src/govoplan_core/privacy/retention.py

@@ -17,6 +17,7 @@ from govoplan_core.core.campaigns import (
     CampaignPolicyContextProvider,
     CampaignRetentionProvider,
 )
+from govoplan_core.core.policy import policy_source_step
 from govoplan_core.core.runtime import get_registry
 from govoplan_access.backend.db.models import Group, User
 from govoplan_audit.backend.db.models import AuditLog
@@ -339,13 +340,13 @@ def _retention_policy_source_fields(patch: dict[str, Any], *, baseline: bool = F
 
 def _retention_policy_source_step(scope_type: str, label: str, scope_id: str | None, patch: dict[str, Any], *, baseline: bool = False) -> dict[str, Any]:
     source_policy = PrivacyRetentionPolicy.model_validate(patch).model_dump(mode="json") if baseline else dict(patch)
-    return {
-        "scope_type": scope_type,
-        "scope_id": scope_id,
-        "label": label,
-        "applied_fields": _retention_policy_source_fields(patch, baseline=baseline),
-        "policy": source_policy,
-    }
+    return policy_source_step(
+        scope_type,
+        label,
+        scope_id,
+        applied_fields=_retention_policy_source_fields(patch, baseline=baseline),
+        policy=source_policy,
+    )
 
 
 def effective_privacy_policy_sources(